Anyone know if the ECU with the self diagnosis light off a GPz1100A1 will be a straight swop onto an older GPz1100B2??
I'm sure I've read somewhere that somebody did it, but a breaker selling an A1 ecu said it wouldn't!?

Cheers!

I doubt it. The B2 ECU has a 15 pin connector, the A1 ECU has 16 pins. And looking at the wiring diagram, the connections are wired in a different order.
Having said that, the extra pin is wired to a four pin multi plug that replaces a 3 pin plug on the B2. Anything is possible, but no, not a straight swap I think.